NI -- no information: don't know anything about the contents of the cat crate.
OTH -- other: you're asked about dogs, not cats, and so the crate doesn't contain a cat.
UNK -- unknown: there is a cat in the crate. Happy now?
ASKU -- asked but unknown : the shipping manifest on the crate is missing.
NAV -- temporarily unavailable : the crate's shipping manifest was sent separately.
NASK -- not asked : no one thought to create a shipping manifest for the crate.
MSK -- masked. It's not a public cat.
NA -- not applicable : You keep asking about dogs?
NP -- not present : there's a blank shipping manifest on the crate, for all the good that does!

Seven flavors of NULL. Wow. It's not just physicists who do "thought experiments"!

Actually, in many DBMS (including SQL Server) you can declare that NULL does equal NULL.

This is sort of like having 2 of Schreodinger's cats in the crates and someone saying, "Is the cats the same color?" and replying, "Sure, if you think so." and then replying the same way when somone asks, "Well, are the cats not the same color?"

Disclaimer: Blog contents express the viewpoints of their independent authors and
are not reviewed for correctness or accuracy by
Toolbox for IT. Any opinions, comments, solutions or other commentary
expressed by blog authors are not endorsed or recommended by
Toolbox for IT
or any vendor. If you feel a blog entry is inappropriate,
click here to notify
Toolbox for IT.